The present application relates to carrier modulation apparatus and, more particularly, to novel apparatus, utilizing a single digital-to-analog converter (DAC), for providing a carrier signal simultaneously modulated with both digital in-phase information and digital quadrature-phase information.
It is well known to transmit information-containing baseband signals, of either digital or analog nature, by the modulation of a carrier signal. The use of a modulator receiving two data streams, with the data of one stream being utilized to modulate an in-phase (I) component of the carrier signal and the second data stream being utilized to modulate a quadrature-phase (Q) component of the carrier signal, is also well known to the art. However, known implementations of such a I-Q modulator require the use of both analog and digital semiconductor circuitry upon the same circuit chip if one were to attempt to implement the I-Q modulator in a monolithically-integrated semiconductor circuit. As there are presently no relatively easy methods of fabricating both digital and analog components upon a semiconductor chip, especially in an integrated circuit of the very-large-scale-integration (VLSI) form, a highly integratable digital I-Q modulator is very desirable.